The present invention relates to a drive circuit for an organic light emitting diode (OLED).
An OLED having a light-emitting layer consisting of an organic compound has been attracting attentions as a device realizing DC low voltage drive. For example, JP-A-6-32307 discloses a structure in which a nodes consisting of a translucent film of an indium tin oxide (ITO) are formed on an upper surface of a substrate consisting of a translucent glass, a hole injection layer, a light-emitting layer, and cathodes consisting of a film of aluminum (Al) are sequentially formed on the anode, and a power supply is connected between the anodes and the cathodes, whereby positive holes generated in the anodes are transmitted to an interface between the hole injection layer and the light-emitting layer, where the positive holes are combined with electrons transmitted from the cathodes to emit a visible ray.
There are known an OLED for performing so-called passive matrix display in which, in the above OLED, the anodes and the cathodes are formed in a plural strip shapes, respectively, and the anodes and the cathodes are arranged in a lattice shape, and one of the anodes and the cathodes are sequentially selected and scanned at a constant time interval with each intersection position of the anodes and the cathodes arranged in the lattice shape as a light emission portion (pixel) and, at the same time, the other of the anodes and the cathodes are driven by a DC constant current circuit serving as a drive source, whereby an arbitrary pixel is caused to emit light, and a driver circuit for the OLED.
Such an OLED has a problem in that, in a long-term use, chargers are accumulated in an intersection between the hole injection layer and the light-emitting layer, whereby a light emission luminance in the pixel falls.
As a technique for solving such a problem, for example, JP-A-9-232074 discloses, as a drive circuit (method) for performing the passive matrix display, a technique with which, at the time of switching to the next scanning line (cathode), all the scanning lines are once connected to a reset voltage zero volt (or power supply voltage) consisting of the same potential for a predetermined time (reset time), whereby a parasitic capacity of the pixels, which should be caused to emit light, is charged by the drive source via drive lines (the anodes) and, at the same time, also charged by a reverse bias voltage of the scanning lines through the parasitic capacity of the pixels, which are not caused to emit light and, consequently, since voltages at both ends of the pixels which should be caused to emit light instantly rise to a potential allowing light emission, the pixels can emit light instantly.
However, connecting all the scanning lines to the reset voltage consisting of the same potential once at the time of switching to the next scanning line makes an operation complex and causes enlargement and complication of a drive circuit. In addition, since the power supply voltage is applied to the unselected scanning lines, an invalid charging current, which does not contribute to light emission, flows to the drive lines via the pixels to increase a consumed current. Further, since all the pixels including the pixels, which should be caused to emit light, are turned off during the reset time, a light emission time is relatively reduced to cause a fall in the light emission luminance. In order to compensate for the fall, a peak luminance should be made higher than usual, which facilitates a luminance fall characteristic to shorten the life of the OLED.
In addition, for example, Japanese Patent No. 3102411 discloses a technique with which a charging circuit for charging the parasitic capacity (junction capacity) to a predetermined potential at the time of rising of drive of the OLED with an output of a pulse generator is provided in constant current drive means for driving the OLED, whereby the junction capacity can be charged in a predetermined time (charging time) and, the OLED is driven without delaying the rising of a pulse, a fall in the light emission luminance can be suppressed.
However, in the correction by the charging circuit, since charges to be cancelled depend upon xe2x80x9ccurrentxc3x97timexe2x80x9d or xe2x80x9cvoltagexc3x97timexe2x80x9d, setting of a current value, a voltage value, and a time, which are control parameters therefor, is difficult. In addition, by providing the charging time, since all the pixels come into a non-light emission state during that time, and all the pixels including the pixels which should be caused to emit light are turned off, a light emission time is relatively reduced to cause a fall in the light emission luminance. In order to compensate for the fall, a peak luminance should be made higher than usual, which facilitates a luminance fall characteristic to shorten the life of the OLED.
The present invention has been devised in view of such points, and it is an object of the present invention to provide a drive circuit which, through application to an OLED for performing the so-called passive matrix display, can extend the life of the OLED with a simple configuration.
The present invention is a drive circuit for an organic light-emitting diode which has anodes and cathodes opposed to each other and an organic layer having at least a light-emitting layer intervening between both the poles, and presents light emission with the opposed portions as pixels, in which capacitors having a predetermined added capacity, to which a bias voltage is applied in a direction of canceling charges to be charged to a parasitic capacity of the pixels, are provided.
In addition, the present invention is a drive circuit for an organic light emitting diode which has plural anodes and plural cathodes intersecting while being opposed to each other and an organic layer having at least a light-emitting layer intervening between both the poles, sets one of both the poles as drive lines and the other of both the poles as scanning lines, and by scanning all of these scanning lines as one field at a predetermined frequency, while sequentially bringing any one of the scanning lines into a selected state, in synchronization with this, connects a drive source to the other of the scanning lines to thereby present light emission with the intersection portions as pixels, in which capacitors having a predetermined added capacity, to which a bias voltage is applied in a direction of canceling charges to be charged to a parasitic capacity of the pixels, are provided.
Further, the present invention is a drive circuit for an organic light emitting diode which has plural anodes and plural cathodes intersecting while being opposed to each other and an organic layer having at least a light-emitting layer intervening between both the poles, sets one of both the poles as drive lines and the other of both the poles as scanning lines, has a partition for insulating the scanning lines from each other with a dielectric material on at least one of both the poles, and by scanning all of these scanning lines as one field at a predetermined frequency, while sequentially bringing any one of the scanning lines into a selected state, in synchronization with this, connects a drive source to the other of the scanning lines to thereby present light emission with the intersection portions as pixels, in which capacitors having a predetermined added capacity, to which a bias voltage is applied in a direction of canceling charges to be charged to a parasitic capacity of the pixels between a conductor film formed on the partition and the one of both the poles, are provided.
In particular, the conductor film is connected to a bias circuit which is commonly connected to supply the bias voltage.
In particular, the sum of the added capacity is equal to or more than the parasitic capacity.
In particular, the drive source performs a DC current or DC voltage drive, and the bias voltage is a DC voltage.